A typical battery pack is characterized by having more than one battery cell. Such packs do not perform, have the same operating characteristics, or life cycle as individual cells. A cell is a single battery unit. During charge and discharge cycles, individual batteries in the pack will often diverge or drift from the pack average or pack target value. Often the pack performance is limited by the weakest or strongest cell during discharge and recharge.
In order to achieve acceptable performance, most battery packs require frequent conditioning cycles and/or an active battery management system. Conditioning cycles bring the pack slowly up to full charge which attempts to equalize the state of the batteries in the pack. To equalize batteries means to reduce the gap between the weakest and strongest cell. Active battery management addresses this issue by providing a small localized charge or discharge across individual cells. Active battery management keeps the strongest and weakest cells closer to the average cell. This results in better pack performance but still well under the performance of an individual cell. Conditioning cycles are still required, but not as often as a pack without a battery management system.
A typical battery management system uses electronic devices such as thermistors or transistors in series or parallel with each cell to locally control the charge or discharge of the cell. Such systems typically dissipate extra power, limit pack capacity, and add expense to pack design and production. This is especially true for large, high power battery cells.
What is needed are circuits and methods to combine battery cells in high power battery packs or power supply systems to improve capacity, charge and discharge rates, lifespan, and other performance characteristics.